<h4>
	Air</h4>
<p>
	In traditional cultures, air is often seen as a universal power or pure substance. Its fundamental importance to life can be seen in words such as aspire, inspire, perspire, and spirit, all derived from the Latin spirare (&quot;to breathe&quot;).</p>
<p>
	Air is one of the four classical elements in ancient Greek philosophy and science. According to Plato, it is associated with the octahedron; air is considered to be both hot and wet. The ancient Greeks used two words for air: aer meant the dim lower atmosphere, and aether meant the bright upper atmosphere above the clouds. Plato, for instance writes that &quot;So it is with air: there is the brightest variety which we call aether, the muddiest which we call mist and darkness, and other kinds for which we have no name....&quot; Among the early Greek Pre-Socratic philosophers, Anaximenes (mid-6th century BCE) named air as the arche (first principle of the world). As it grows warm and rarefied, air becomes fire; as it cools and condenses it becomes water, then earth and rock. A similar belief was attributed by some ancient sources to Diogenes Apolloniates (late 5th century BCE), who also linked air with intelligence and soul (psyche), but other sources claim that his arche was a substance between air and fire. Aristophanes parodied such teachings in his play The Clouds by putting a prayer to air in the mouth of Socrates.</p>
<p>
	Air was one of many archai proposed by the Pre-socratics, most of whom tried to reduce all things to a single substance. However, Empedocles of Acragas (c. 495-c. 435 BCE) selected four archai for his four roots: air, fire, water, and earth. Ancient and modern opinions differ as to whether he identified air by the divine name Hera, Aidoneus, or even Zeus. Empedocles&rsquo; roots became the four classical elements of Greek philosophy. Plato (427-347 BCE) took over the four elements of Empedocles. In the Timaeus, his major cosmological dialogue, the Platonic solid associated with air is the octahedron which is formed from eight equilateral triangles. This places air between fire (four triangular sides) and water (twenty triangular sides), which Plato regarded as appropriate because it is intermediate in its mobility, sharpness, and ability to penetrate. He also said of air that its minuscule components are so smooth that one can barely feel them.</p>
<p>
	Content from <a class="external-link" href="http://en.wikipedia.org/wiki/Air_%28classical_element%29" rel="nofollow">Wikipedia</a></p>
